1. Field of the Invention
The present invention relates to an optical disc reproduction method and an optical disc reproduction apparatus for obtaining an optical disc identification information.
2. Description of the Prior Art
Currently, an optical disk recording medium called DVD (Digital Video Disc/Digital Versatile Disc) is under development. This DVD disc is capable or recording a wide range of data including a video data, audio data, and computer data. The DVD, in spite of its small size identical to a CD (Compact Disc), has a large recording capacity by the techniques of small-pitch recording tracks and data compression.
There are several DVD disc families such as a DVD-ROM (Read Only Memory) disc dedicated to reproduction; a DVD-R (Recordable) disc to which a data can be written once; and a DVD-RAM (Random Access Memory) disc.
In the development of the DVD-ROM disc, it has been suggested to provide a BCA (Burst Cutting Area) for the purpose of providing information for identifying each of the DVD-ROM discs.
A BCA code (signal) is recorded on the aforementioned DVD-ROM disc, after a predetermined video data or the like is recorded, by partially removing with a laser beam an aluminium film which has been deposited as a reflection film. That is, a BCA code is formed by removing an aluminium film of an area not affecting reproduction of a video data, audio data, or computer data which has been recorded as a pit signal on the disc.
More specifically, the BCA code is recorded so as to be overwritten on a pit string of dummy data recorded on an area located along the inner circumference of the disc.
As shown in FIG. 1, the BCA is recorded as bar-code stripes in the cicumferential direction of the optical disc, each stripe having a length of about 1 mm between 22.3 (+0/-0.4) mm to 23.50.+-.0.05 mm from the center of the center hole of the disc. This code is recorded by way of RZ modulation method and is read out by an optical pickup serving for reproducing video data or audio data recorded on the optical disc.
Here, as shown in FIG. 2A, the aforementioned BCA area on the DVD-ROM disc consists of aluminium surfaces on which aluminium is deposited and areas from which the aluminium film has been removed by the laser beam. These areas are continuous to one another in the circumferential direction of the disc. As shown in FIG. 2B. an RF signal read out by scanning this BCA area has slits of the BCA code and mirror modulation caused by scanning the mirror surface by the laser spot.
In order to extract the BCA code alone from this RF signal, the RF signal is subjected to a processing for removing a high-frequency band component. As a result, as shown in FIG. 2B, a waveform affected by mirror modulation appears. In this case, it is impossible to set an appropriate threshold level for binarization, which in turn disables to extract a correct BCA code.